Vacuum switch tubes are needed in applications requiring stand-off of high voltages (e.g. on the order of 500V to 6 kV DC) and fast switching of large currents (e.g. on the order of 300 A to 20 kA). Such applications can include triggering of air-bags, the initiation of explosives, control of high energy physics equipment, power supplies and capacitive discharge units (CDUs). Vacuum switch tubes are typically configured to provide an open circuit, non-conducting condition between a current source and a load. The tube is activated (e.g. switch closed) by a triggering signal to affect an electric discharge within the tube, switching the tube to a closed circuit conducting condition, thereby allowing the passage of current from the source to the load. Further discussion of the operation of vacuum switch tubes can be found for example, in U.S. Pat. No. 5,739,637 to Boettcher, and in “Investigation into Carbon-Trigger Vacuum Switches for High-Voltage, High-Current Switch Applications”, by K. J. Bunch, et al., presented at the 7th IEEE International Vacuum Electronics Conference (IVEC) Apr. 25-27, 2006, Monterey, Calif., the entirety of each of which is herein incorporated by reference
The assembly of vacuum switch tubes typically requires piece-part hand assembly by highly skilled craft workers which makes them too expensive for many applications. Additionally, piece-part hand assembly of individual units (e.g. individuals fabricated serially) results in variations in assembly which can affect the part to part uniformity of the device's operational characteristics. What are needed are methods for batch fabrication (e.g. a plurality fabricated simultaneously) of vacuum switch tubes to
The present invention addresses this need for batch fabrication of vacuum switch tubes by providing methods that comprise stacking an assembly of layers comprising a plurality of tube sub-assemblies, aligned through one or more common layers, and heating the assembly of layers in a vacuum oven to affect joining (e.g. bonding) of the individual layers into a cohesive structure. Joining can be accomplished by methods such as; traditional metallization of ceramics followed by brazing, active metal brazing without the use of ceramic metallizations, or direct brazing methods, again not requiring the use of ceramic metallizations. The latter two approaches yield an additional reduction in the cost of units produced, by eliminating the processing steps and costs associated with producing metallized layers on bare ceramics. Additional descriptions of the traditional metallization and brazing, active metal brazing and direct brazing methods can be found for example in: “Comparison of Metal-Ceramic Brazing Methods”, by C. A. Walker et al., presented at the 36th International Brazing and Soldering Symposium, Chicago, Ill., Nov. 13-14, 2007, the entirety of which is incorporated herein by reference.
The bonded structure can then be singulated (e.g. by dicing, laser scribing, sawing etc.) to separate out the individual vacuum switch tubes. The vacuum joining process can produce an evacuated environment (e.g. on the order of 1×10(−7) mmHg) in the vicinity of the anode, cathode and trigger electrodes of the vacuum switch. The methods according to the present invention, by employing a stacked assembly of layers, provides for fabricating a plurality of switch tubes simultaneously in a batch fabrication approach, greatly eliminating hand assembly and piece part counts, thereby reducing the cost of producing a vacuum switch tube. Methods according to the present invention additionally reduce the spread in operational characteristics on a part to part basis, compared to methods based on traditional hand assembly of individual units. Methods according to the present invention can further reduce the cost of switch tubes by employing joining (e.g. brazing) processes that do not require the metallization of ceramic components.